Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

S. Sinha-Roy ¹, M. Mohanty ¹, G. Malhotra ¹, V. P. Sharma ¹, D. W. Joshi ¹

Affiliations
1 Geological Survey of India, 15-16 Jhalana Dungri, Jaipur 302 004, IN

Abstract

The Proterozoic sequences of South-Central Rajasthan are contained in the Lower to Middle Proterozoic Aravalli and Middle to Upper Proterozoic Delhi fold belts. The stratigraphic relations within these fold belts as well as the basement-cover relations are beset with several problems. The conglomerate horizons have been studied to address some of these problems. Based on the conglomerate horizons, representing erosional unconformities, the Aravalli Supergroup has been sub-divided into three groups and the Delhi Supergroup of the South Delhi fold belt into two groups with constituent formations. These horizons are also useful in identifying three stages of basin evolution for the Aravalli fold belt. The Middle Aravalli Conglomerate is the most prominent representing mid-Aravalli hiatus, and corresponding to the Debari Transgressive Stage which followed the Delwara Rifting Stage in the Lower Aravalli in a system of ensialic distensional tectonics where triple-junctions and pull-apart basins are formed. The Upper Aravalli has been the Jharol Ocean Opening Stage, the oceanic/transitional crust having been consumed at a median ultramafic suture line during the formation of the Aravalli fold belt. The South Delhi fold belt has also multi-stage development history with the Barr Conglomerate representing the base of the youngest Delhi sequence.

Keywords

Proterozoic, Conglomerate, Aravalli Fold Belt, Delhi Fold Belt, Rajasthan, Basin Evolution.

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P. R. Golani ¹, D. Bhattacharyya ², S. Sanyal ², I. R. Kirmani ², G. Malhotra ², S. Bhattacharyya ², A. K. Grover ², J. L. Narang ²

Affiliations
1 Geological Survey of India, A.M.S.E. Wing, Central Zone, Seminary Hills, Nagpur - 440 006, IN
2 Geological Survey of India, Western Region, 15-16, Jhalana Dungri, Jaipur - 302 004, IN

Abstract

The Deldar-Kui-Chitrasani (DKC) fault is a brittle structure manifested by anastomosing system of fractures in the southwestern part of the South Delhi Fold Belt (SDFB). Based on the identification of cross-fibre and 'jigsaw puzzle' type structures, presence of vugs lined with cryptocrystalline quartz, replacement of calcite by chalcedonic quartz and evidences of argillic alteration, the breccia along the fault is recognised by present workers as epithermal breccia. Lithogeochemical sampling of the breccia reveals that, besides moderate base metal signatures, gold values are consistently present in significant concentrations comparable to regional anomalies associated with epithermal gold deposits in the United States. In view of the high proportion of magmatic rocks in the southwestern part of the SDFB, the DKC fault zone is considered a favourable target for searching epithermal type of gold mineralisation.

Keywords

Economic Geology, Epithermal Breccia, Lithogeochemistry, Gold Anomaly, Faults, Shear Zone, South Delhi Fold Belt, Rajasthan, Gujarat.

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S. Sinha-Roy ¹, G. Malhotra ¹

Affiliations
1 Geological Survey of India, A-4, Vijay Path, Jaipur 302004, IN

Abstract

In the Jahazpur belt of SE Rajasthan, the Proterozoic Jahazpur cover sequence of dolomite, BIF, orthoquartzite and tuffaceous carbonaceous phyllite unconformably overlies the Archaean basement comprising granite-greenstone sequences of the Hindolis and the Mangalwar Complex. The Jahazpur rocks developed in ensialic aborted rifts. Structures of four deformations in the basement rocks and of three deformations in the cover rocks have been recognised, the first deformation of the basement rocks being pre-Jahazpur in timing. The first and the second regional folds in the Jahazpur sequence have produced type-2 interference pattern. The original orientation of the first fold was almost E-W. The second fold, trending NE-SW, reoriented the first deformation structures, and controlled the linear trend of the belt. The unconformity between the cover and the basement has been modified by thrusting.

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